Wellbore cement having polymer capsule shells

Abstract

Capsules with a cement additive covered by a polymeric outer shell are added to wellbore cement. The additive is released from the shells by osmosis or shell ruptures. Capillary forces draw the additive into micro-annuli or cracks present in the cement, where the additive seals the micro-annuli and cracks to define a self-sealing material. The empty shells remain in the cement and act as an additive that modifies cement elasticity. The capsules are formed by combining immiscible liquids, where one of the liquids contains a signaling substance, and each of the liquids contains a reagent. When combined, the liquids segregate into a dispersed phase and a continuous phase, with the dispersed phase having the signaling agent. The reagents react at interfaces between dispersed and continuous phases and form polymer layers encapsulating the signaling agent to form the capsules. Adjusting relative concentrations of the reagents varies membrane strength and permeability.

What is claimed is: 
     
       1. A method of wellbore operations comprising:
 forming capsules comprising an encapsulant encased within polymeric shells by a polycondensation reaction in which a first reagent of a first fluid is polymerized with a second reagent of a second fluid, the second fluid being immiscible within the first fluid; 
 controlling permeability of the polymeric shells by adjusting concentrations of the first and second reagents so that the polymeric shells are permeable by the encapsulant, and the encapsulant is released from the polymeric shells by osmosis; 
 forming a slurry comprising a cement and the capsules; 
 urging the slurry into an annular space between a sidewall of the wellbore and a tubular in the wellbore; 
 curing the slurry in the wellbore to create a set cement in the wellbore that seals against and adheres to the tubular and the sidewall to form sealing and adhering interfaces between the set cement and both of the tubular and sidewall, and in response to displacement of one of the tubular or sidewall, the set cement correspondingly undergoes deformation to retain the sealing and adhering interfaces; and 
 monitoring the wellbore for the release of the encapsulant from the capsules. 
 
     
     
       2. The method of  claim 1 , controlling a release rate of the encapsulant from the polymeric shells by changing a viscosity of one of the first or second fluids. 
     
     
       3. The method of  claim 1 , wherein the deformation of the set cement causes a stress in the set cement, wherein the stress at a threshold magnitude ruptures at least some of the polymeric shells to form spent capsules. 
     
     
       4. The method of  claim 3 , wherein the presence of the spent capsules in the set cement further increases elasticity of the set cement. 
     
     
       5. The method of  claim 1 , where the encapsulant is released from the polymeric shells by osmosis to form empty polymeric shells, and where the empty polymeric shells form spent capsules. 
     
     
       6. The method of  claim 1 , where the encapsulant comprises a signaling agent selected from the group consisting of colored dyes, fluorophore, isotopes, fluorescent dyes, fluorescein, and combinations thereof. 
     
     
       7. The method of  claim 6 , further comprising monitoring the presence and concentration of the signaling agent that releases from the polymeric shells. 
     
     
       8. The method of  claim 1 , where the encapsulant comprises a cement sealing reagent. 
     
     
       9. The method of  claim 1 , where interfacial polymerization occurs between the first and second reagents. 
     
     
       10. The method of  claim 9 , where the first and second reagents comprise compounds having a reactive functional group and are selected from the group consisting of monomers with tri-functional acid chlorides and monomers with di-functional amino groups. 
     
     
       11. The method of  claim 9 , where the first reagent further comprises sebacoyl chloride. 
     
     
       12. The method of  claim 9 , further comprising controlling a release rate of the encapsulant from within the polymeric shells by the adjusting of the concentrations of the first and second reagents. 
     
     
       13. The method of  claim 1 , where the polymeric shells comprise a polymer selected from the group consisting of poly(ethylene trimesoylamide), poly-(para-phenylene trimesoylamide), poly-(meta-phenylene trimesoylamide), poly(hexamethylene trimesoylamide), and poly(hexamethylene-co-sebacoyl trimesoylamide).